Hearing aids are portable hearing apparatuses which are used to cater for the hard of hearing. Different hearing aid designs such as behind-the-ear hearing aids (BTE), hearing aid with external receiver (RIC: receiver in the canal) and in-the-ear hearing aids (ITE), for example also concha hearing aids or canal hearing aids (ITE, CIC), are provided in order to accommodate the numerous individual needs. The hearing aids listed by way of example are worn on the outer ear or in the auditory canal. However there are also bone conduction hearing instruments, implantable or vibrotactile hearing aids available on the market. The damaged hearing is stimulated either mechanically or electrically in this case.
As fundamental components hearing aids basically comprise an input transducer, an amplifier and an output transducer. The input transducer is usually a sound pick-up, for example a microphone, and/or an electromagnetic receiver, for example an induction coil. The output transducer is usually implemented as an electroacoustic transducer, for example miniature loudspeaker, or as an electromechanical transducer, for example bone conduction receiver. The amplifier is conventionally integrated in a signal processing unit. FIG. 1 shows this basic construction using the example of a behind-the-ear hearing aid. One or more microphone(s) 2 for picking up the sound from the environment are fitted in a hearing aid housing 1 for wearing behind the ear. A signal processing unit 3, which is also integrated in the hearing aid housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker or receiver 4 which emits an acoustic signal. The sound is optionally transmitted, via a sound tube which is fixed to an otoplastic in the auditory canal, to the eardrum of the apparatus wearer. The hearing aid, and in particular the signal processing unit, is supplied with power by a battery 5 that is also integrated in the hearing aid housing 1.
An unpleasant effect when wearing a hearing aid is that the wearer's own voice sounds unnatural. This is due to the fact that the wearer's own voice is conducted into the auditory canal via bone conduction and causes a certain sound pressure there, in particular at lower frequencies. If the auditory canal is open the corresponding compression waves can be conducted to the outside. If the auditory canal is closed by the hearing aid however, then a higher sound pressure builds up here which is called the occlusion effect and since it is unnatural is deemed unpleasant.
A generic method for actively reducing occlusion in hearing aids is known from document WO 2004/021740 A1 and document WO 2006/037156 A1. The first document describes the transducer transmission function from the input of the receiver via the auditory canal to the output of the auditory canal microphone in more detail. It can be determined very accurately in situ using the hearing aid as a measuring instrument. The transducer transmission function is complex, i.e. a function of absolute value and phase over frequency.
In an incompletely adaptive implementation of actively reducing occlusion the measured transducer transmission function is used to determine in a computer the optimum configuration of digital signal processing for actively reducing occlusion. This optimization process could basically also take place completely automatically. However there is the problem here of the algorithm being irreversibly incorrectly changed in certain situations, or of a great deal of computing time being required. Manual intervention is necessary or helpful in these situations.